The present invention is directed to a setting tool for driving fastening elements into a receiving material by means of highly compressed gases. The fastening elements are driven in the driving direction from the tool into the receiving material. The tool includes a piston guide extending in the driving direction and forming a guiding borehole in which a driving piston is axially displaceably positioned. The driving piston has a head at one end and a shaft extending axially from the head in the driving direction. Means are provided within the guiding borehole for returning the driving piston to its starting position after a fastening element has been driven. The means is in the form of at least one spring element and at least one damping element adjoining the spring element with the spring element located between a stop on the piston guide and an end surface of the driving piston head facing in the driving direction.
Setting tools, operated by highly compressed gases, are used for driving nail-shaped fastening elements into hard receiving materials, such as concrete, rock, steel and the like. In one type of such a setting tool, widely used at the present time and preferred for safety reasons, the highly compressed gases act on a driving piston which, in turn, drives a fastening element into the receiving material. On one hand, such a tool has particular advantages, on the other, there is the disadvantage after each driving in step, the driving piston must be returned into its starting position. Accordingly, for many years persons expert in the field have been concerned with providing means for returning the driving piston to its starting position.
The NO-PS 84 159 discloses a setting tool operated by an explosive powder charge. The driving piston in this tool can be pushed back into its starting position after each driving step by a restoring element in the form of a compression spring. The compression spring surrounds the shaft of the driving piston and extends between a stop on the piston guide facing opposite to the driving direction and an end surface on the head of the driving piston facing in the driving direction.
The direct return of the driving piston of the setting tool by means of a compression spring leads to problems, since very high displacing speeds of the driving piston are required for the driving-in step. The problem is that the displacing speed is higher than the running speed of a malfunction within the compression spring. This means that, at the start of each driving-end step, the coils of the compression spring, which do not lie in contact with the head of the driving piston, do not find out in good time that a movement of the compression spring has commenced and, therefore, do not recede, so that the head of the driving piston or the coils in motion impact at full speed against the coils which have not receded. At the same time, a high vibration energy is introduced into and accumulated in the compression spring, and causes strong and uncontrolled vibrations of the spring. Furthermore, at the transition in the coil, where the coils have collided with the piston and the part of the coil which has not been actuated, a very high bending stress develops, which can lead to breakage of the compression spring.